1. Field of the Invention
The present invention generally relates to a communication system, and more particularly to a system and method for allocating a channel in a communication system.
2. Description of the Related Art
With the development of cellular type wireless mobile telecommunication systems in the U.S. at the end of the 1970's, a voice communication service began to be provided to users through an Advanced Mobile Phone Service (AMPS) system serving as a first generation (1G) analog type mobile communication system. A Code Division Multiple Access (CDMA) system serving as a second generation (2G) mobile communication system was commercialized to provide users with voice and low rate data services in the middle of the 1990's.
An International Mobile Telecommunication-2000 (IMT-2000) system serving as a third generation (3G) mobile communication system has been partially commercialized to provide improved wireless multimedia services, global roaming, and high rate data services from the end of the 1990's. In particular, the 3G mobile communication system has been developed to provide high rate data as an amount of service data increases quickly in the mobile communication system.
The 3G mobile communication system has evolved into a fourth generation (4G) mobile communication system. The 4G mobile communication system is being standardized to provide efficient interworking with wired and wireless communication networks and an integrated service as well as the simple wireless communication service provided by the previous generation communication system. Thus, technologies are needed to provide large capacity data in wireless communication networks as in wired communication networks.
Active research is being conducted on an Orthogonal Frequency Division Multiplexing (OFDM) scheme and an Orthogonal Frequency Division Multiple Access (OFDMA) scheme useful for transmitting high rate data on wired/wireless channels in the 4G mobile communication system. According to the OFDM scheme, a multicarrier is used to transmit data. The OFDM scheme is a type of Multi Carrier Modulation (MCM) scheme in which a serial symbol stream is converted into parallel symbol streams and is modulated into multiple subcarriers, i.e., multiple subcarrier channels that are orthogonal to each other.
A mobile communication system for transmitting data using a multicarrier is a system in which one OFDM symbol is divided into subcarriers such that multiple users employ the subcarriers. The mobile communication system employs multiple subcarriers. Among the multiple subcarriers, some subcarriers are employed as pilot subcarriers. Except for the pilot subcarriers, the remaining subcarriers are employed as data subcarriers. Further, the mobile communication system divides the data subcarriers in a unit of a predetermined number of subcarriers, generates subchannels, and allocates the generated subchannels to multiple users according to the system.
Subchannels mean a channel including of multiple subcarriers. Consequently, the mobile communication system aims to obtain a frequency diversity gain by distributing all used subcarriers, particularly data subcarriers, over a total frequency band. A structure of the mobile communication system using the above-described multicarrier is illustrated in FIG. 1.
The mobile communication system has a single cell structure. The mobile communication system is configured with a Base Station (BS) 100 and Mobile Stations (MSs) 110, 120, 130, 140, and 150 managed by the BS 100.
Environments of channels measured by the MSs 110, 120, 130, 140, and 150 are independent of each other due to shadowing loss, path loss, MS movement, etc., and are time-variant. Because of the above-described channel characteristics, the BS 100 allocates subchannels to the MSs while considering the channel environments, thereby increasing data transmission efficiency of the overall system. The BS 100 applies an Adaptive Modulation and Coding (AMC) scheme while considering reception channel environments of the MSs 110, 120, 130, 140, and 150. That is, a high efficiency modulation and coding scheme is applied when a channel environment is good, whereas a low efficiency modulation and coding scheme is applied when a channel environment is bad. A channel allocation process of the mobile communication system is illustrated in FIG. 2.
The mobile communication system includes a BS 200 and K MSs 250. K is the total number of MSs located in a service area of the BS, i.e., a cell.
The BS 200 transmits a Channel Quality Information (CQI) request to the K MSs 250 for receiving a service therefrom in step 201. In response to the CQI request, the MSs 250 measure CQI of respective subchannels. At this time, each MS selects a predetermined number of subchannels with a better CQI among the measured subchannels.
Then, the MSs 250 feed back the measured CQI to the BS 200 in step 203. The CQI reported by each MS is the CQI of the selected subchannels. The MSs 250 transmit the CQI to the BS 200 in a regular period.
When the CQI is transmitted, the MSs 250 transmit information about the selected subchannels in the form of a bitmap in which a selected subchannel is set to a bit of 1 and an unselected subchannel is set to a bit of 0. When the subchannels selected by the MS are successive, a value of a start subchannel index and, for example, a value of N representing the number of subchannels selected by the MS are transmitted together with the CQI. According to whether the subchannels selected by the MS are successive, information about the selected subchannels is transmitted to the BS 200.
The BS 200 receives the CQI and the subchannel information and performs a channel allocation process, i.e., a subchannel allocation process, using the CQI and the subchannel information in step 205.
The BS 200 transmits channel allocation information to an associated MS according to the channel allocation process in step 207. When the channel allocation scheme as illustrated in FIG. 2 is employed, the BS 200 should receive the CQI of all MSs located in the service area thereof. In the current mobile communication system, a channel state of subchannels allocated to each MS is continuously varied. The respective MSs should feed back the varied CQI of the subchannels so the BS 200 can perform the channel allocation process.
However, there is a problem in that an operation for frequently feeding back CQI of subchannels of all MSs leads to signaling overhead and a signaling operation for feeding back the CQI of the subchannels leads to uplink interference in the mobile communication system.
Thus, a need exists for a method for efficiently performing a channel allocation process while supporting a high-speed mobile communication service in a mobile communication system.